Methods of detecting signals from subjects using hydro-insensitive alternating current responsive composites

ABSTRACT

An alternating current responsive composite is disclosed. The composite includes a polymeric material and a polar material that is substantially dispersed within the polymeric material. The polar material is responsive to the presence of an alternating current.

PRIORITY INFORMATION

The present application claims priority to U.S. Provisional PatentApplication Ser. No. 60/371,306 filed Apr. 10, 2002.

BACKGROUND OF THE INVENTION

The invention relates to polymeric materials that are used to conductelectrical signals, and relates in particular to conductive adhesivesthat are used with medical monitoring sensors that are placed directlyon a patient, such as an electro-cardiogram (EKG) sensor.

Electrically conductive pressure-sensitive adhesives for use inbiomedical applications are disclosed, for example, in U.S. Pat. No.4,848,353. Since such conductive materials typically depend on thepresence of water, however, the material must be maintained in a sealedenvironment until being used. See also, U.S. Pat. No. 5,143,071, whichdiscloses non-stringy adhesive gels for that are hydrophilic.

Such substances must be isolated from the environment prior to use(e.g., in sealed packages), and may function improperly if allowed tolose water from the conductive material. These limitations adverselyaffect both the cost of sensors that use such conductive adhesives aswell as the amount of use that any particular sensor may enjoy.

There is a need therefore, for a material that may be used to conductelectricity yet is not susceptible to variations in the water vaporcontent of the environment in which it is used.

SUMMARY OF THE INVENTION

The invention provides an alternating current responsive composite. Thecomposite includes a polymeric material and a polar material that issubstantially dispersed within the polymeric material. The polarmaterial is responsive to the presence of an alternating current. Invarious embodiments, the polar material includes an organic salt and thepolymeric material includes a pressure sensitive acrylic adhesive.

BRIEF DESCRIPTION OF THE DRAWING

The following description may be further understood with reference tothe accompanying drawings in which:

FIG. 1 shows an illustrative diagrammatic view of a composite inaccordance with an embodiment of the invention;

FIG. 2 shows an illustrative diagrammatic top view of a monitoringsensor using a composite in accordance with an embodiment of theinvention;

FIG. 3 shows an illustrative diagrammatic side view of the monitoringsensor shown in FIG. 2 taken along line 3-3 thereof;

FIG. 4A shows an illustrative diagrammatic graphical representation of apatent signal being monitored by a conventional hydro-gel sensor;

FIG. 4B show illustrative diagrammatic graphical representation of apatent signal being monitored by a sensor in accordance with anembodiment of the invention;

FIG. 4C shows an illustrative diagrammatic graphical representation of apatent signal being monitored by a sensor including a polymeric materialbut no polar material; and

FIG. 5 shows an illustrative diagrammatic top view of a conductor padusing a composite in accordance with an embodiment of the invention; and

FIG. 6 shows an illustrative diagrammatic side view of the conductor padshown in FIG. 5 taken along line 6-6 thereof.

The drawings are shown for illustrative purposes and are not to scale.

DETAILED DESCRIPTION OF THE INVENTION

It has been discovered that a polar material (such as an organo salt)may be dispersed within a polymeric material of sufficient concentrationthat the resulting composite may be responsive to the presence of analternating current yet not be sensitive to water gain or loss fromambient temperature or humidity conditions. For example, as shown inFIG. 1, a composite 10 may include an organo salt 12 that is dispersedwithin a polymeric material 14. If the organo salt 12 has crystallizedout of the polymeric material or has bloomed to the surface, then thesalt is not compatible with that given polymer, thus the non-homogenoussystem will not respond to pick up the alternating current signal. If,on the other hand, the salt becomes dissolved within the polymericmaterial (rendering the polymeric material clear), then the twomaterials are compatible, and a substantially homogenous mixture existsto form the desired alternating current responsive blend. When the saltis compatible with the polymer blend, it responds to the rise of analternating current signal by orienting with the field then returning toa ground state with the collapse of the alternating current field. Byresponding to the presence of an electric field, therefore, thecomposite acts as a capacitor in coupling the signal (within a patient)to a sensor.

A suitable combination of polar material and polymeric material may beidentified by the following procedure. First, a polar material iscombined with the polymeric material in about five differentconcentrations (typically between about 5% to about 45% by weight). Thenthe adhesive-salt composite is drawn onto a release liner (of about 1.5mil), and permitted to dry and cure. The surface of the composite isthen inspected after a short period of time. If the salt hascrystallized out or bloomed to the surface, then the combination ofcomponents is not compatible. If, on the other hand, the composite isclear, it is subject to the next level of compatibility testing. Thesamples should then be subjected an exposure test in which the samplesare exposed to 100 F with 95% relative humidity for 3 days. The samplesare then again inspected to determine whether the polar material hasmigrated toward either surface. If there has been no migration of thepolar material and the composite is clear, then the dielectric constantfor the composite is determined and the composite is tested for use as amedical monitoring material. The dielectric constant, for example, maybe at least 50 for signals at 200 Hz.

In accordance with an embodiment of the invention, the polymericmaterial may include an acrylic pressure sensitive adhesive such as theV-95 acrylic pressure sensitive adhesive sold by FLEXcon Corporation ofSpencer, Mass. The polar material may include a quaternary ammoniumorgano salt such as the CHEMAX AS-3106 sold by Chemax Corporation ofBeaumont, Tex. The percentage by weight of the polar material in thecomposite may for example, range from about 5% to about 65%, andpreferably ranges from about 10% to about 35%.

As shown in FIGS. 2 and 3, the composite 10 may be used with medicaldiagnostic sensor pads in which a metallic contact element 16 issurrounded by the composite 10 and coupled to monitoring equipment via aconductor 18. The element 16 and composite 10 are positioned within anadhesive polyethylene foam carrier 20. In use, the sensor pad is placedon a patient's skin and internal alternating current signals (such as aheart rate) are received by the element 16 through the composite 10 andcoupled to the monitoring equipment.

In further embodiments, the composite 10 may be used in a wide varietyof other uses, including for example, other diagnostic sensors, as wellas applications in fuel cell technology, battery technology, electroluminescence, or any other application in which an electrical currentand/or signal is carried through an electrolyte that has at it's sourcea dependence on water. Composites of the invention are insensitive tothe presence or absence of water vapor, and therefore, do not requirehigh levels of maintenance of certain levels of water in packaging andduring use. It has been discovered that the shortcomings of having anelectrolyte dependent on the presence of water vapor are avoided byusing for example organo-salts (quaternary ammonium salts,organo-sulfates, fluoroboarates, and other salt like materials havingsome organic functionality). The organic functionality facilitates thesalt's organic compatibility with the polymeric material. Organiccompatibility may not be required when a polymer has compatibility witha purely inorganic salt, e.g., Cesium Iodide. An objective is to providea polar material such as salt that is at least substantially uniformlydispersed throughout the polymeric material. The water insensitiveelectrolytic may then respond to an ascending/collapsing electric fieldvia a capacitive coupling. In view of the relatively high volume directcurrent resistance of this type of doped polymer, the sensitivity istowards alternating current (AC) rather than direct current (DC). Thecomposite, therefore, may even be more effective at detecting an ACsignal than carrying an electrical current.

As discussed above with reference to FIGS. 2 and 3, composites of theinvention may be used in place of electrolytic gels such as hydro-gelsin cardiac monitoring pads. The monitoring pad with a composite of theinvention described above was used to monitor a person's heart rate andthe received signal was compared to signals received using aconventional hydro-gel electrolyte and using the polymeric materialwithout doping with a polar material. As shown in FIG. 4B, the receivedsignal using a composite of the invention (as shown at 24 in FIG. 4A)provided a nearly identical signal as the conventional hydro-gelelectrolyte sensor (as shown at 22 in FIG. 4A). FIG. 4C shows that thereceived signal 26 using the polymeric material alone provided nodiscernable signal information.

Another variation of these monitoring pads is to provide a polymericmaterial that has sufficient adhesive qualities to be used itself as theadhesive without requiring the adhesive foam carrier 20. As shown inFIGS. 5 and 6, a conductor pad for use in medical applications mayinclude a composite 30 of the invention that is sufficiently adhesivethat no additional adhesive is required to maintain contact between apatient's skin and the pad. In this example, the pad used as a conductorto provide electrical signals via conductor 28 to a metallic conductorelement 32. The alternating current field is then coupled to the patientvia the composite 30 via the capacitive coupling characteristics of thecomposite. A supporting material 34 may also be used to providestructural integrity.

Composites of certain embodiments of the invention have also been testedat varying humidity and over extended periods of time and found toexhibit an insignificant amount of change in performance. Suchcomposites have also been found to provide a recovery time afterinducing an overloading current of within 5-10 seconds after theoverloading condition was ceased. Although both the hydro-gel andcomposites of the invention act as a parallel capacitor/resistor, thehydro-gel has a DC resistance of about 500 ohms while a doped adhesiveof the invention has a DC resistance of about 100K ohms or higher. Thehydro-gel has a capacitance in both high (˜10 kHz) and low (˜200 Hz)frequency ranges in the microfarad range. The doped adhesive of anembodiment of the invention has a more pronounced capacitance that vaneswith frequency effect from about 230 Pico-farads at 10 kHz to about 1microfarad at 200 Hz. The dielectric constant K must, therefore, bechanging with frequency. In fact, at 10 kHz it is discovered that K isabout 10, and at 200 Hz, K is about 10,000 or above. When the K is lowerthe resistance increases, which requires that the pad impedance andmatching impedance of the monitoring equipment must be increased.

In other embodiments, the polymeric material may include variouspolymeric materials such as acrylic adhesives that may be distinguishedby the relative composition of their monomers and by their molecularweights. For example, acrylic adhesives such as the DURO-TAK 80-1074acrylic adhesive, the DURO-TAK 80-136A acrylic adhesive, or the DURO-TAK87-2852 acrylic adhesive each of which sold by National Starch andChemical Co. of Bridgewater, N.J. may be used as the polymeric material.In certain embodiments, the polar material may include organo-sulfonium,organic ester salts, organo-metallic materials, organo-borates,phosphates and phosphites etc. In particular, the polar material mayinclude a quaternium 18 & isopropyl alcohol (such as the ARQUAD 2HT-75product), dicocodimoium chloride & isopropyl alcohol (such as the ARQUAD2C-75 product), stearyl octyldimonium methosulfate (such as the ARQUADHTL8-MS product) each of which is sold by Akzo Nobel Surface ChemistryLLC of Chicago, Ill., or PEG-5 cocomonium chloride (such as the ETHOQUADC/25 product sold by Brenntag N.V. of Deerlijk, Belgium). Suitablefurther specific combinations of polymeric materials and salts areprovided in the following table using the above product names.

Percent Polar Polar Material Polymeric Material Material by WeightARQUAD 2HT-75 87-2852 20% ARQUAD 2HT-75 87-2852 40% ARQUAD 2C-75 87-285220% ARQUAD 2C-75 87-2852 40% ARQUAD 2C-75 80-136A 20% ARQUAD 2C-7580-136A 40% ARQUAD HTL8-MS 87-2852 20% ARQUAD HTL8-MS 87-2852 40% ARQUADHTL8-MS 80-136A 20% ARQUAD HTL8-MS 80-136A 40% ETHOQUAD C/25 87-2852 20%ETHOQUAD C/25 87-2852 40% ETHOQUAD C/25 80-136A 20% ETHOQUAD C/2580-136A 40%

Composites of the invention may be employed in a wide variety ofapplications involving the coupling of alternating current electricalactivity from one location to another, such as other applicationsinvolving the monitoring of electrical activity, or the activeapplication of electrical activity, or even the grounding of undesiredelectrical activity in, for example, conductive housings.

Those skilled in the art will appreciate that numerous modifications andvariations may be made to the above disclosed embodiments withoutdeparting from the spirit and scope of the invention.

1.-13. (canceled)
 14. A method of detecting an output signal that isrepresentative of an alternating electrical signal from a subject, saidmethod comprising the steps of: providing a monitoring sensor on saidsubject, said monitoring sensor including a conductive element and acomposite material that includes a polar material that is substantiallydispersed within a polymeric material; receiving the alternatingelectrical signal from the subject such that said composite changes itsdielectric constant responsive to alternately ascending and collapsingvoltages of the alternating electric signal from the subject; andproviding an output signal via the conductive element responsive tochanges in the dielectric constant of the composite that arerepresentative of the alternating electric signal from the subject. 15.The method as claimed in claim 14, wherein said polar material is asalt.
 16. The method as claimed in claim 14, wherein said polar materialis an organic salt.
 17. The method as claimed in claim 14, wherein saidpolymeric material is an adhesive.
 18. The method as claimed in claim14, wherein said polymeric material is an acrylic adhesive.
 19. Themethod as claimed in claim 14, wherein said polymeric material is apressure sensitive adhesive.
 20. The method as claimed in claim 14,wherein said polymeric material includes a concentration of said polarmaterial of between about 5% and about 65% based on weight.
 21. Themethod as claimed in claim 14, wherein said polymeric material includesa concentration of said polar material of between about 10% and about35% based on weight.
 22. A method of detecting an output signal that isrepresentative of an alternating electrical signal from a subject, saidmethod comprising the steps of: providing a monitoring sensor on saidsubject, said monitoring sensor including a conductive element and acomposite material that includes a polar material that is substantiallydispersed within a polymeric material; receiving the alternatingelectrical signal from the subject such that said composite has adielectric constant that changes from a first dielectric constant to asecond dielectric constant when the alternating electrical signal fromthe subject is increasing; and providing a discharge signal from thecomposite to the conductive element when the alternating electricalsignal from the patient is decreasing, wherein successive dischargesignals provide the output signal that is representative of thealternating electric signal from the subject.
 23. The method as claimedin claim 22, wherein said polar material is a salt.
 24. The method asclaimed in claim 22, wherein said polar material is an organic salt. 25.The method as claimed in claim 22, wherein said polymeric material is anadhesive.
 26. The method as claimed in claim 22, wherein said polymericmaterial is an acrylic adhesive.
 27. The method as claimed in claim 22,wherein said polymeric material is a pressure sensitive adhesive. 28.The method as claimed in claim 22, wherein said first dielectricconstant is about
 10. 29. The method as claimed in claim 22, whereinsaid second dielectric constant is at least about 10,000.
 30. The methodas claimed in claim 22, wherein said polymeric material includes aconcentration of said polar material of between about 5% and about 65%based on weight.
 31. The method as claimed in claim 22, wherein saidpolymeric material includes a concentration of said polar material ofbetween about 10% and about 35% based on weight.
 32. A method ofdetecting an output signal that is representative of an alternatingelectrical signal from a patient, said method comprising the steps of:providing a monitoring sensor on said patient, said monitoring sensorincluding an adhesive that includes a polar material that issubstantially dispersed within a polymeric material; receiving thealternating electrical signal from the patient such that said adhesivehas a dielectric constant that changes from a first dielectric constantto a second dielectric constant that is higher than the first dielectricconstant when the alternating electrical signal from the patient isincreasing; and providing a discharge signal from the adhesive when thealternating electrical signal from the patient is decreasing, whereinsuccessive discharge signals provide the output signal that isrepresentative of the alternating electric signal from the patient. 33.The method as claimed in claim 32, wherein said first dielectricconstant is about 10 and wherein said second dielectric constant is atleast about 10,000.